Self-Aligned Insulated Film for High-K Metal Gate Device

ABSTRACT

A method forming a gate dielectric over a substrate, and forming a metal gate structure over the semiconductor substrate and the gate dielectric. The metal gate structure includes a first metal material. The method further includes forming a seal on sidewalls of the metal gate structure. The method further includes forming a dielectric film on the metal gate structure, the dielectric film including a first metal oxynitride comprising the first metal material and directly on the metal gate structure without extending over the seal formed on sidewalls of the metal gate structure.

This application is a continuation of U.S. patent application Ser. No.15/717,520 filed Sep. 27, 2017, which is a continuation of U.S. patentapplication Ser. No. 14/989,351 filed Jan. 6, 2016, now issued as U.S.Pat. No. 9,779,947, which is a continuation of U.S. patent applicationSer. No. 14/471,293 filed Aug. 28, 2014, now issued as U.S. Pat. No.9,252,224, which is a divisional of U.S. patent application Ser. No.13/244,365 filed Sep. 24, 2011, now issued as U.S. Pat. No. 8,822,283,which claims the benefit of provisional application Ser. No. 61/530,845filed Sep. 2, 2011, the disclosures of which are hereby incorporated byreference in their entirety.

BACKGROUND

Semiconductor device fabrication includes many different processes, eachprocess having associated cycle-time and cost requirements. It is acontinued desire to reduce cost and cycle-time in device fabrication.Further, it is a continued desire to reduce the number of defects andimprove yields in semiconductor fabrication. One area for improvement isthe fabrication of metal-oxide-semiconductor field-effect transistor(MOSFET) devices having a high dielectric constant (high-k) metal gate.The present disclosure provides improvements that relate to thefabrication of such devices.

SUMMARY

The present disclosure provides many different embodiments of methodsfor making integrated circuit devices. In one embodiment, a method ofmaking an integrated circuit includes providing a semiconductorsubstrate and forming a gate dielectric over the substrate, such as ahigh-k dielectric. A metal gate structure is formed over thesemiconductor substrate and the gate dielectric and a thin dielectricfilm is formed over that. The thin dielectric film includes oxynitridecombined with metal from the metal gate. The method further includesproviding an interlayer dielectric (ILD) on either side of the metalgate structure.

In another embodiment, a method for making an integrated circuitincludes providing a substrate with a high-k dielectric and providing apolysilicon gate structure over the high-k dielectric. A hardmask isformed on a top surface of the polysilicon gate structure and sidewallstructures on side surfaces of the polysilicon gate structure. Afterforming the hardmask, a doping process is performed on the substrateadjacent to the polysilicon gate structure. After the doping processes,the hard mask and the polysilicon gate structure are removed, keeping atleast a portion of the sidewall structures to form a trench. The trenchis filled with at least one metal material to form a metal gate, such ascopper, aluminum, titanium, and/or tantalum. A thin dielectric layer isthen formed on and self aligned with a top surface of the metal gate,the thin dielectric layer including the metal material.

The present disclosure also provides many different embodiments ofintegrated circuit devices. In one embodiment, an integrated circuitincludes a semiconductor substrate and a gate dielectric over thesubstrate, such as a high-k dielectric. A metal gate structure is overthe semiconductor substrate and the gate dielectric, and a dielectricfilm is on the metal gate structure. The dielectric film includesoxynitride combined with metal from the metal gate. An interlayerdielectric (ILD) is on either side of the metal gate structure.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion. Also, several elements and featuresare shown in the figures, not all of which are numbered for the sake ofclarity. It is understood, however, that symmetrical features and itemswill be similarly situated.

FIG. 1 is a flowchart of a method of making the semiconductor devicehaving a metal gate stack according to one embodiment of the presentinvention.

FIGS. 2-15 are sectional views of one embodiment of a semiconductordevice having an n-type and p-type MOSFET (an NFET and PFET) with metalgate stacks, at various fabrication stages constructed according to themethod of FIG. 1.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof various embodiments. Specific examples of components and arrangementsare described below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a first feature over or on a second featurein the description that follows may include embodiments in which thefirst and second features are formed in direct contact, and may alsoinclude embodiments in which additional features may be formedinterposing the first and second features, such that the first andsecond features may not be in direct contact.

FIG. 1 is a flowchart of a method 100 for making a semiconductor deviceaccording to one embodiment. The semiconductor device includes an n-typefield-effect transistor (NFET) and a p-type field-effect transistor(PFET), both with a metal gate stack resistor constructed according tovarious aspects of the present disclosure. FIGS. 2 through 15 aresectional views of a semiconductor structure 200 at various fabricationstages and constructed according to one or more embodiments. Thesemiconductor structure 200 and the method 100 of making the same arecollectively described with reference to FIGS. 1 through 16.

Referring to FIGS. 1 and 2, the method 100 begins at step 102 byproviding a semiconductor substrate 201 on which to form a polysilicongate. The semiconductor substrate 201 includes silicon. Alternatively,the substrate includes germanium, silicon germanium or other propersemiconductor materials. The semiconductor substrate also includesvarious doped regions such as n-well and p-wells. The semiconductorsubstrate 201 includes an isolation feature such as shallow trenchisolation (STI) 202 formed in the substrate to separate NFET and PFETtransistors. The formation of the STI feature includes etching a trenchin a substrate and filling the trench by one or more insulator materialssuch as silicon oxide, silicon nitride, or silicon oxynitride. Thefilled trench may have a multi-layer structure such as a thermal oxideliner layer with silicon nitride filling the trench. In one embodiment,the STI feature 202 is created using a process sequence such as: growinga pad oxide, forming a low pressure chemical vapor deposition (LPCVD)nitride layer, patterning an STI opening using photoresist and masking,etching a trench in the substrate, optionally growing a thermal oxidetrench liner to improve the trench interface, filling the trench withCVD oxide, using chemical mechanical planarization (CMP) to etch back,and using nitride stripping to leave the STI structure. Thesemiconductor substrate 201 also includes various n-wells and p-wellsformed in various active regions.

Two similar polysilicon gate stacks 204, 206 are formed on the substrate201, on either side of the STI structure 202. In the present embodiment,each polysilicon gate stack 204, 206 includes (viewed in the figure fromthe substrate 201 up), a silicon oxide interfacial layer (IL), a high-kdielectric layer (HK) and a cap layer, generally designated with thereference number 214. In various embodiments, the interfacial layer maybe formed by chemical oxide technique, thermal oxide procedure, atomiclayer deposition (ALD) or chemical vapor deposition (CVD). The high kdielectric material layer may be formed by CVD, ALD, plasma enhanced CVD(PE CVD), or plasma enhanced ALD (PEALD). The cap layer can be formedusing CVD with precursor silane (SiH4) or other silicon based precursor.

Continuing with the present embodiment, a polycrystalline silicon(polysilicon) layer 216 is formed above the IL/HK/Cap layer 214. In thepresent embodiment, the polysilicon layer 216 is non-doped. The siliconlayer 216 alternatively or additionally may include amorphous silicon.An oxide 218 is formed over the polysilicon layer 216, and a siliconnitride layer (SiN) 218 is formed over it, forming a hard mask (HM). Itis understood that the formation, including patterning, of such layersis well known in the art, and will not be further discussed for the sakeof brevity and clarity.

Referring to FIGS. 1 and 3, the method 100 proceeds to step 103, where aSiN seal 230 is formed around the gate stacks 204, 206. In the presentembodiment, the SiN seal 230 is formed using atomic layer deposition toform a layer of approximately 50 A thickness. In addition, the substrate201 is doped to form halogen and light doped drain (LDD) regions for thesource and drain (S/D) features. The source and drain regions are formedfor the NFET and the PFET devices using proper doping species.

Referring to FIGS. 1 and 4, the method 100 proceeds to step 104, where amain side wall (MSW) is formed. The MSW includes an oxide (OX) layer 232adjacent to the outer surface of the SiN layer 230 and the upper surfaceof the substrate 201. In the present embodiment, the OX layer 232 isformed by ALD to a thickness of about 30 A. The MSW also includes SiNsidewalls 234 formed on an outer surface of the OX layer 232. The SiNlayer is formed to a maximum thickness of about 250 A. As shown in FIG.4, the MSW is adjacent to the sidewalls of the polysilicon gate stacks204, 206, and do not cover the entire substrate.

Referring to FIGS. 1 and 5, the method 100 proceeds to step 105, whereS/D and electrostatic discharge regions 240 are fully implanted andactivated. As mentioned above with respect to step 103, LDD regions werepreviously provided in the substrate 201 prior to the MSW being formedat step 104. At step 105, a deeper implantation process is performed.The doped regions for the NFET are doped with P-type dopants, such asboron or BF2, and the doped regions for the PFET are doped with N-typedopants, such as phosphorus or arsenic. The doped regions 240 may beformed directly on the substrate 201, in a P-well structure, in anN-well structure, in a dual-well structure, or using a raised structure.In the present embodiment, the S/D activation is performed by a laseranneal (LSA) at about 1150 C., along with a rapid thermal anneal (RTA)with about a 1010 C. spike.

Referring to FIGS. 1 and 6, the method 100 proceeds to step 106, inwhich Nickel silicide (NiSi) regions 242 are formed for future contactsto the S/D regions 240. In the present embodiment, Ni is deposited to athickness of about 400 A in the substrate 201, guided by the MSW formedat step 105.

Referring to FIGS. 1 and 7, the method 100 proceeds to step 107, inwhich a portion of the SiN layer 234 of the MSWs is removed from the twogate stacks. As shown in FIG. 7, a portion of the SiN layer, now labeled244, remains on the MSWs, as well as the OX layer 232. In the presentembodiment, this removal process is performed by a wet etch using H₃PO₄at about 12 C. In addition, the HM 218, 220 is removed from the topportion of the polysilicon gate 216. In the present embodiment, the SiNand OX HM is removed by a dry etch process.

Referring to FIGS. 1 and 8, the method 100 proceeds to step 108, inwhich an interlayer dielectric (ILD) layer 250 is formed over the twogate stacks 204, 206. In the present embodiment, a tensile SiN contactetch stop layer 252 is deposited first, to a thickness of about 200 A.Thereafter, the ILD layer 250, phosphate silicate glass (PSG) in thepresent embodiment, is deposited to a thickness of about 2000 A usingand ion plasma (IPM).

Referring to FIGS. 1 and 9, the method 100 proceeds to step 109, inwhich the upper surface of the device is planarized to expose thepolysilicon gates 216. In the present embodiment, a chemical mechanicalpolishing process is performed.

Referring to FIGS. 1 and 10, the method 100 proceeds to step 110, inwhich one of the two polysilicon gate stacks 204, 206 is masked. In thepresent embodiment, the polysilicon mask 216 for the NFET gate stack 204is masked with a patterned photoresist (PR) layer 260. Specifically, a20 A TiN hard mask 262 is deposited over a top surface of the device,and then the PR layer 260 is deposited over it. The PR layer 260 ispatterned to mask the NFET gate stack 204.

Referring to FIGS. 1 and 11, the method 100 proceeds to step 111, thepolysilicon 216 in the PFET gate stack 206 is removed. In the presentembodiment, the polysilicon 216 is removed via etching from the PFETgate stack 206 (which is now more accurately described as a trench thana gate stack), while the polysilicon in the NFET gate stack remainsintact for being shielded by the patterned PR 260 in FIG. 10.Afterwards, a metal gate 266 is formed in the trench remaining from theremoved polysilicon 216 in the PFET gate stack 206. The metal gate canbe formed of one or more layers, and in the present embodiment, includethe following deposited metals in order: TaN, TiN, TaN, TiN and Al (withtrace amounts of Cu). The deposited metal layers cover the entiresurface of the device 200, but are then removed, including the PR 260,by a CMP process.

Referring to FIGS. 1 and 12, the method 100 proceeds to step 112, inwhich a similar process is repeated on the NFET gate stack 204. In thepresent embodiment, since the polysilicon has already been removed andreplaced on the PFET gate stack 206, a patterned PR layer covering thePFET gate stack is not used. The polysilicon 216 is removed from theNFET gate stack 204, such as by an etch process. Afterwards, a metalgate 268 is formed in the trench remaining from the removed polysilicon216 in the NFET gate stack 204. The metal gate 268 can be formed of oneor more layers, and in the present embodiment, include the followingdeposited metals in order: TaN, TiAl, TiN and Al (with trace amounts ofCu). The deposited metal layers cover the entire surface of the device200, but are then removed, including the PR 260, by a CMP process. As aresult, both of the polysilicon gate stacks are now metal gate stacks204, 206.

Referring to FIGS. 1, 13 a, and 13 b, the method 100 proceeds to step113, in which ultra-thin metal oxynitride films 288, 286 are formed onthe top surface of the metal gate stacks 204, 206, respectively. In oneembodiment, an oxygen plasma at 20 C., 900 W, 60 sec, with O2, isbombarded onto the surface. Afterwards, an Ammonia plasma at 400 C., 75W, 60 sec, with NH3/N2, is bombarded onto the surface. In an alternativeembodiment, a nitrogen plasma (without NH3) can be used. The result isan ultra-thin metal oxynitride film, with a thickness of about 1 nm toabout l0nm. The oxynitride films only react with the metal materials(e.g., Ti, Ta, Cu, Al, TiAl) in the gate stacks 204, 206, thereby makingthe process self-aligned.

Referring to FIGS. 1 and 14, the method 100 proceeds to step 114, inwhich an ILD 290 is formed over the metal gate stacks 204. 206,including the ultra-thin metal oxynitride films 288, 286. In the presentembodiment, the ILD 290 is undoped silicate glass (USG) at a thicknessof about 1450 A. The USG 290 is formed by a deposition process at 400 C.using SiH4/N2O/He. The USG 290 can be formed on top of the PSG 250, orthe PSG 250 can be removed, and/or a additional combinations ofdielectric materials can be formed.

Referring to FIGS. 1 and 15, the method 100 proceeds to step 115,contact are formed for electrical connection to the S/D regions of theNFET and PFET transistors. In the present embodiment, contact openingsare patterned and etched in the ILD 290, and then filled with W plugs292. The upper surface of the device is planarized by CMP, resulting inthe device as shown in the Figure. From there with back end of lineprocessing.

The present embodiments discussed above provides many benefits, it beingunderstood that other embodiments may not have the same benefits. Thebenefits of the embodiments discussed above include improved reliabilitydue to the plasma-induced ultra-thin insulator layer, as opposed toalternative methods for forming such a layer. Also, chip-level cellstress is improved. Further, yield improvement and reduced shorts areprovided by transforming any metal residue (e.g., Al, Cu, Ti, or Ta)into the metal oxynitride.

The present disclosure is not limited to applications in which thesemiconductor structure includes a FET (e.g. MOS transistor) and may beextended to other integrated circuit having a metal gate stack. Forexample, the semiconductor structures may include a dynamic randomaccess memory (DRAM) cell, an imaging sensor, a capacitor and/or othermicroelectronic devices (collectively referred to herein asmicroelectronic devices). In another embodiment, the semiconductorstructure includes FinFET transistors. Of course, aspects of the presentdisclosure are also applicable and/or readily adaptable to other type oftransistor, including single-gate transistors, double-gate transistorsand other multiple-gate transistors, and may be employed in manydifferent applications, including sensor cells, memory cells, logiccells, and others.

The foregoing has outlined features of several embodiments. Thoseskilled in the art should appreciate that they may readily use thepresent disclosure as a basis for designing or modifying other processesand structures for carrying out the same purposes and/or achieving thesame advantages of the embodiments introduced herein. Those skilled inthe art should also realize that such equivalent constructions do notdepart from the spirit and scope of the present disclosure, and thatthey may make various changes, substitutions and alterations hereinwithout departing from the spirit and scope of the present disclosure.

What is claimed is:
 1. A method comprising: forming a gate dielectricover a substrate; forming a metal gate structure over the semiconductorsubstrate and the gate dielectric, the metal gate structure comprising afirst metal material; forming a seal on sidewalls of the metal gatestructure, the seal being substantially uniform in thickness; forming adielectric film on the metal gate structure, the dielectric filmincluding a first metal oxynitride comprising the first metal materialand directly on the metal gate structure without extending over the sealformed on sidewalls of the metal gate structure.
 2. The method of claim1, wherein forming the metal gate structure includes forming a firstportion of the gate structure comprising the first metal material and asecond portion comprising a second metal material that is different thanthe first metal material.
 3. The method of claim 2, wherein forming themetal gate structure includes forming a third portion comprising a thirdmetal material different from the first metal material and the secondmetal material.
 4. The method of claim 1, wherein the first metalincludes copper and the dielectric film includes copper oxynitride. 5.The method of claim 1, wherein: the first metal material includes atleast one from the group consisting of titanium, tantalum, and aluminum;and the metal gate structure includes copper and titanium.
 6. The methodof claim 5, wherein the dielectric film further includes at least onefrom the group consisting of titanium oxynitride, tantalum oxynitride,aluminum oxynitride, and titanium aluminum oxynitride.
 7. The method ofclaim 1, wherein forming the thin dielectric film includes performing aplasma bombardment process on the oxynitride that causes the oxynitrideto react with metal from the metal gate structure and form the firstmetal oxynitride.
 8. The method of claim 7, wherein the dielectric filmcombines with the copper to form copper oxynitride and with the titaniumto form titanium oxynitride.
 9. A method comprising: forming a gatedielectric over a substrate; forming a metal gate structure over thesemiconductor substrate and the gate dielectric, the metal gatestructure comprising a first portion comprising a first metal and asecond portion comprising a second metal that is different than thefirst metal; forming a seal on opposing sidewalls of the metal gatestructure, the seal being substantially uniform in thickness; forming athin dielectric film disposed directly on the metal gate structure, thethin dielectric film comprising metal oxynitride, the thin dielectricfilm covering a top surface of the metal gate structure withoutextending over the seal; and forming an interlayer dielectric (ILD) oneither side of the metal gate structure.
 10. The method of claim 9,wherein the gate dielectric is a high-k dielectric.
 11. The method ofclaim 9, wherein the metal gate structure includes copper and titanium.12. The method of claim 9, wherein the thin dielectric layer has athickness less than about 10 nm.
 13. The method of claim 9, wherein themetal gate structure includes at least two from the group consisting ofcopper, titanium, tantalum, and aluminum.
 14. The method of claim 13,wherein the thin dielectric film includes at least two from the groupconsisting of copper oxynitride, titanium oxynitride, tantalumoxynitride, aluminum oxynitride, and titanium aluminum oxynitride.
 15. Amethod, comprising: forming a trench between two sidewall structures;forming a seal on opposing sidewalls of the trench, the seal beingsubstantially uniform in thickness forming a metal gate within thetrench, the metal gate comprising a first metal material; forming a thinnitride-containing layer on a top surface of the metal gate such thatthe thin dielectric layer covers the metal gate structure withoutextending over the sidewall structures.
 16. The method of claim 15,wherein the first metal material includes copper and the first metaloxynitride of the thin nitride-containing layer includes copperoxynitride.
 17. The method of claim 15, wherein the metal gate furtherincludes a second metal material that is different from the first metalmaterial, and the thin nitride-containing layer includes a second metaloxynitride comprising the second metal material.
 18. The method of claim17, wherein the first metal material and the second metal materialinclude at least two from the group consisting of copper, titanium,tantalum, and aluminum.
 19. The method of claim 18, wherein the thindielectric layer includes at least two from the group consisting ofcopper oxynitride, titanium oxynitride, tantalum oxynitride, aluminumoxynitride, and titanium aluminum oxynitride.
 20. The method of claim15, wherein the thin dielectric layer has a thickness less than about 10nm.